When you’ve already had a baby, you might feel like a seasoned pro during your next pregnancy—what could possibly surprise you? Well, as Chrissy Teigen is finding out, things can be completely different with every pregnancy.

Teigen recently announced that she’s expecting her second child with her husband John Legend. And, this past weekend, she took to Twitter to talk about how this pregnancy is already different than when she was carrying her daughter, Luna. “Can someone just be honest with me and tell me if it's normal to get bigger, faster with second baby? Because I am getting big, fast, and everyone's go-to is ‘it's that second baby!’ but they're lying. I know it,” she wrote. “I can handle the truth just tell me. It's not normal is it?”

Several moms sympathized with her in the comments and many said that family and strangers kept asking if they were carrying twins the second time around because they developed a bump faster than in the past.

There are actually a few solid biological reasons for why this happens.

Often with a first pregnancy, women don’t start “showing” until around 20 weeks, Melissa Goist, M.D., an ob/gyn at The Ohio State University Wexner Medical Center, tells SELF. But with subsequent pregnancies, this can happen around 13 weeks. One reason for this is your rectus abdominis muscles, a.k.a. your abs.

When you get pregnant the first time, those muscles are pretty strong and keep your uterus inside your pelvis for a longer period of time so you don’t appear as big, Yvonne Bohn, M.D., an ob/gyn at Providence Saint John’s Health Center in Santa Monica, Calif., tells SELF. “With the second baby, the muscles have been stretched so the uterus pops out faster,” she explains. “It gives women the appearance that they’re getting bigger, faster.”

So, you won't necessarily gain more weight with a second pregnancy, but you might look further along at an earlier stage, Christine Greves, M.D., a board-certified ob/gyn at the Winnie Palmer Hospital for Women and Babies, tells SELF. That means you might feel more bloated or like you're "pouching out," she says, "but there’s not an actual increase in fat cells.”

Your body also knows the drill with subsequent pregnancies, so it responds faster, Jessica Shepherd, M.D., an assistant professor of clinical obstetrics and gynecology and Director of Minimally Invasive Gynecology at The University of Illinois College of Medicine at Chicago, tells SELF. “It goes through the routine much quicker than with your first pregnancy, where your body is really trying to figure out what’s going on,” she says.

But the main thing to remember is that every pregnancy is different.

Hormones can influence you differently from pregnancy to pregnancy and the fact that you’re carrying two totally different children at different times in your life makes a difference, too, women’s health expert Jennifer Wider, M.D., tells SELF. Plus, there’s also the not-so-tiny fact that you’re also caring for a child this time around. You might have been able to nap as soon as you got home from work during your first pregnancy or lay on the couch watching Netflix when you felt like crap, that’s not your reality now. “It’s harder on your body,” Dr. Greves says.

However, keep in mind that growing faster the second time around says nothing about your health or fitness. "Even in the healthiest, most fit women, the core/abdominal muscles have reduced strength," Dr. Goist says. And, although you may grow more quickly in the earlier stages of your pregnancy, you also might taper off in the second and third trimesters, Dr. Shepherd points out. Ultimately, though, that doesn’t matter. “Focus on the process rather than the body changes,” she says.

If your body's changes are concerning, definitely check in with your doctor for some reassurance. But you don't need to automatically assume that something is wrong (or that you're having twins) if things are going a little faster or slower this time around. “Remove expectations, focus on exercising and eating healthy, and let nature take its course,” Dr. Wider says. “This is one of those things not totally in your control.”